Fuel tanks are subject to pressure and vacuum changes due to differences between atmospheric pressure around the tank body and the pressure of a gaseous mixture of air and fuel vapor in the fuel tank body. For example, when gas pressure in the tank body exceeds atmospheric pressure, the top of the tank body may expand away from the bottom of the tank body. When atmospheric pressure exceeds the gas pressure in the tank body, the top of the tank body may collapse toward the bottom of the tank body. Pressure and vacuum changes experienced by a fuel tank may increase when sealed evaporation control (EVAP) systems are employed to reduce evaporative emissions and fuel leakage, e.g., in hybrid electric vehicles. Such tanks may thus be manufactured from thick steel to withstand pressure and vacuum builds that occur in a sealed tank over a diurnal temperature cycle.
In order to reduce vehicle weight and thus improve battery life and fuel economy, fuel tanks may be made of light-weight materials such as plastics. Such tanks are prone to deflection and deformation when subjected to increased pressure or vacuum. As such, the tank may include rigid structural elements within the fuel tank body in addition to various non supportive components such as sensors and fuel delivery components. Structural elements may be strategically placed to support regions of the fuel tank that are most likely to deflect due to pressure differentials.
However, in the event of a vehicle crash, such structural elements are prone to breaking. This compromises the structural integrity of the fuel tank, increasing the likelihood of fuel tank deformation. This may result in damage to a plastic fuel tank that breaches the walls of the tank, leading to unwanted emissions and/or fuel leakage. As such, being able to diagnose a damaged or degraded structural support is imperative as fuel tank design trends to light-duty enclosures.
Other attempts to address deformation of plastic fuel tanks include correlating fuel level, fuel tank pressure, and other fuel tank parameters. One example approach is shown by Criel et al. in U.S. 2014/0298885. Therein, a method for estimating fuel tank deformation is presented using on-board sensors coupled to the fuel tank. However, Criel does not provide means for determining whether the deformation is indicative of the degradation of structural supports. As such, damage to the fuel tank may go unnoticed as long as the fuel level is within a plausible range.
In one example, the issues described above may be addressed by a fuel system that comprises a fuel tank including at least a top wall, a bottom wall, and one or more stanchions positioned within the fuel tank, each stanchion coupled to the top wall and the bottom wall. A strain gauge is positioned on the outside of the fuel tank, opposite an intersection of a stanchion and the top wall, such that degradation of the stanchion results in results in pressure-dependent deformation of the fuel tank that is registered by the strain gauge. In this way, degradation of deformable fuel tanks, such as polymeric fuel tanks, may be diagnosed and indicated.
As one example, following an indication of a vehicle collision, the strain gauges may be read along with the ambient temperature. After a duration in which the ambient temperature changes significantly, the strain gauges may be read again. Significant deviation in strain gauge output over this period may be indicative of a broken stanchion, thus allowing the vehicle operator to be alerted to the potential problem.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.